1. Field of the Invention
An aspect of the present invention relates to a voltage generation circuit, and more particularly, to a voltage generation circuit provided in a semiconductor integrated device.
2. Description of the Related Art
As a voltage generation circuit provided in a semiconductor integrated device, a voltage generation circuit called a ½ VAA generator has been used as a power supply for a memory circuit, such as a DRAM (dynamic random access memory) (for example, see JP-A-2003-22136). The ½ VAA generator drops an internal voltage VAA, which is obtained by decreasing a power supply voltage, by half.
In recent years, with a reduction in the driving voltage of the memory circuit, demands for a voltage generation circuit capable of generating a lower internal voltage VAA and a half voltage VAA/2 have increased.
The voltage generation circuit disclosed in JP-A-2003-22136 includes a first operational amplifier including an input stage having a pair of p-channel MOS transistors and a current mirror circuit having a pair of n-channel MOS transistors, a second operational amplifier including an input stage having a pair of n-channel MOS transistors and a current mirror circuit having a pair of p-channel MOS transistors, and an output circuit having a p-channel MOS transistor and an n-channel MOS transistor that are connected in series to each other between a power supply line and a ground line.
A first reference voltage is applied to an inverting input terminal (−) of the first operational amplifier, and a half voltage is applied to a non-inverting input terminal (+) thereof. An output voltage of the first operational amplifier is supplied to the gate of the n-channel MOS transistor.
A second reference voltage that is lower than the first reference voltage is applied to an inverting input terminal (−) of the second operational amplifier, and a half voltage is applied to a non-inverting input terminal (+) thereof. An output voltage of the second operational amplifier is supplied to the gate of the p-channel MOS transistor.
In the voltage generation circuit disclosed in JP-A-2003-22136, when the internal voltage VAA is low, a voltage Vgsp between the gate and the source of each of the pair of p-channel MOS transistors of the first operational amplifier is lower than a threshold voltage Vthp, or a voltage Vgsn between the gate and the source of each of the pair of n-channel MOS transistors of the second operational amplifier is lower than a threshold voltage Vthn. As a result, errors occur in the voltage generation circuit.
To operate the voltage generation circuit at a low driving voltage, it is considered to reduce the threshold voltages of the pair of p-channel MOS transistors of the first operational amplifier and the pair of n-channel MOS transistors of the second operational amplifier. However, when the threshold voltage is lowered, a leakage current from the MOS transistor increases.